Casing structural integrity and failure modes in a range of well types: a review.

This paper focus on factors attributing to casing failure, their failure mechanism and the resulting failure mode. The casing is a critical component in a well and the main mechanical structural barrier element that provide conduits and avenue for oil and gas production over the well lifecycle and beyond. The casings are normally subjected to material degradation, varying local loads, induced stresses during stimulation, natural fractures, slip and shear during their installation and operation leading to different kinds of casing failure modes. The review paper also covers recent developments in casing integrity assessment techniques and their respective limitations. The taxonomy of the major causes and cases of casing failure in different well types is covered. In addition, an overview of casing trend utilisation and failure mix by grades is provided. The trend of casing utilisation in different wells examined show deep-water and shale gas horizontal wells employing higher tensile grades (P110 & Q125) due to their characteristics. Additionally, this review presents casing failure mixed by grades, with P110 recording the highest failure cases owing to its stiffness, high application in injection wells, shale gas, deep-water and high temperature and high temperature (HPHT) wells with high failure probability. A summary of existing tools used for the assessment of well integrity issues and their respective limitations is provided and conclusions drawn

Plug and abandonment of oil and gas wells: a comprehensive review of regulations, practices, and related impact of materials selection.

This paper reviews the state of research in permanent barrier materials for plug and abandonment of oil and gas wells to identify key strengths and weaknesses of each barrier material and understand the impact of reservoir conditions and fluids on barrier failures. The influence of regulatory requirements on P and A practices and the impact of selected barrier material on possible repurposing of depleted reservoirs for hydrogen and CO2 storage are also discussed. This review reveals that previous studies in these areas have focused primarily on improving plug placement and durability without significant consideration of the potential for long term development of leakage paths in the old wellbore infrastructure (cement and casing) whose surfaces remain exposed to reservoir fluids below the permanent plug after conventional P and A. The need for a new approach to plug and abandonment materials selection and reengineering of materials placement methods to ensure permanent isolation of reservoir fluids from existing well infrastructure is herein identified especially as the stock of wells nearing their end of life grows on a global scale. A summary of studies in the accelerated degradation of Portland cement in the presence of corrosive reservoir fluid under high temperature and pressure conditions is also presented. This will significantly drive research in materials selection for alternative barrier as HPHT wells mature for permanent abandonment

Multicriteria material selection for casing pipe in shale gas wells application.

The conventional method of casing selection is based on availability and/or order placement to manufacturers based on certain design specifications to meet the anticipated downhole conditions. This traditional approach is very much dependent on experience as well as constructing oil and gas wells at minimum budget. However, this material selection approach is very limited in meeting the requirement of shale gas wells. This study utilises the material performance indices and ANSYS Granta database to examine three different casing pipe buckling scenarios including the buckling with corrosion potentials and buckling with impact and long-term service temperature conditions. Consequently, numerical evaluations of the response of the selected casing materials established the stress, deformations, and safety factor for the first scenario (shale gas well with buckling tendencies). The significance of this new method is added advantage in terms of integrating materials' physicochemical, thermal and mechanical properties and the casing functional performance to establish ideal selection within the design space or requirements. Results obtained in this study shows that there are optional materials that outperform the most common casing grades (P110 &Q125) utilised in shale gas development in terms of both safety and cost. This study established a procedure between cost, safety, performance indices and materials' physical and mechanical properties for a typical well design scenario. This procedure will assist the design engineer justify the selection of a particular material(s) safely and technically for a given shale well casing application in future. In all the 10 materials investigated, even though the P110 (API casing grade) meets the buckling design scenario and widely used in shale gas well development, there are many alternative viable material candidate options that outperform P110 Grade with the best material candidate studied in this work being BS 145

Stress analysis of pipe-in-pipe systems under free span for deep water pipeline applications.

This study examined the phenomena of free span for a pipe -in- pipe (PIP) system for pipeline application. Two different span length of 8 and 30 meters are modelled and simulated using nonlinear stress analysis. The effect of pressure, temperature and gravity on the PIP system are determined and compared with conventional single pipeline. From the results obtained, it is clear that the finite element analysis (FEA) results correlated very well with those calculated using analytical methods. Percentage differences were generally less than 10%, with some discrepancies which were due to assumption of thin-walled theory which assumes a radial stress equals to zero, whereas the FEA calculates a non-zero radial stress. The key finding in this study demonstrated the strong potentials of PIP system in terms of structural reliability for deep-water pipeline application. Specifically, the 30m single pipe in free span (with pressure and temperature) deflected 205.1mm, more than double the corresponding PIP. This knowledge can be beneficial to selection and design considerations for pipeline system responses to both the gravity, thermal and pressure loading as well as the potential failure modes that may results in a typical scenario. Various theoretical calculations of stresses are used to validate the finding in this study of the single pipe and PIP models for flat seabed and free span

Structural response of a compliant pipe-in-pipe under frictionless and frictional conditions of the seabed.

Pipe-in-Pipe (PIP) technology has been studied significantly owing to its superior performance in deep-water and high-pressure high temperature fields than conventional single pipe. The PIP system has excellent track record of mitigating flow assurance problems from subsea wells through maintenance of the fluid's temperature in the pipe. It has also been applied in marine environment where conventional single pipe cannot perform. However, owing to complex interaction and contact within the PIP system and seabed, the mechanism of load transfer and the stresses that developed due to pressure, temperature and combined loading has not been fully understood and quantified. Therefore, this study examined the effect of pressure, temperature and the combined loading on PIP systems for flat seabed subsea pipeline. Simulations are performed to examined frictional and frictionless conditions of the flat seabed on PIP system and individual results of inner pipe, insulation material and outer pipe are presented for each analysis. The analytical calculations are carried-out for determining the operating stresses in each component of the PIP system in view of its significance for the overall structural behaviour of the system and validation of the numerical model. The impact response of the inner pipe, insulation and the outer pipe based on pressure, temperature and the combination of both (pressure and temperature) and the resulting stress on each component of the PIP system are investigated and the result presented. Furthermore, results of axial, radial and hoop stresses for the individual loading condition and with coupled analysis corresponding to each simulation (Frictional and Frictionless seabed conditions) are found to be closely similar with percentage difference less than 5 except for the von Mises stress which give 5.3%. This interesting finding revealed that the friction force does not affect structural integrity of the PIP system compared to conventional - single pipeline assuming all other parameters remains constant. Moreover, the presence of the outer pipe and the insulation material enhanced the performance of the inner pipe. The numerical simulation predicts closely the impact response for pipe-in-pipe composite specimens under individual and combined loading conditions. Therefore, the results obtained will serve as a reference guide for designing, construction and operating PIP system in the future to develop unconventional challenging energy resources like High Pressure High Temperature fields

Quasi-static compression tests of overwrapped composite pressure vessels under low velocity impact.

Pressure Vessels are being utilised in different applications that are indispensable including automobile, aerospace, underwater vehicles, oil and gas, chemical engineering among other applications. However, there is lack of knowledge on the influence of induced damage and the resulting performance of such vessels under quasi-static loading and axial compression. Specifically, the vessels studied in this study is made up of a high-density polyethylene liner and glass fibre overwraps. Therefore, this research investigated the load bearing capacities and the energy absorbed of the indented vessels in axial and hoop directions to determine the resistance of the vessels after such damaged using experiment, and damage characterisation microscopy, non-destructive testing and analysis. Quasi-static transverse and axial compression testing was performed on composite cylinders made of polyethylene liner and glass fibre overwraps. Both quasi-static and axial compression tests were performed with the Instron Machine 3382, quasi-static compression was performed at speed of 500 mm/min, while the axial compression test was performed at speed of 2.5 mm/min. The results for the damage profile and the effect on compressive strength of the composite damaged and two non-damaged cylinders was found to be relatively similar. Additionally, the results demonstrate that the quasi-static compression have little or no influence on the axial strength of the cylinders. The microscopic and Dolphicam2 results for damage characterisation on the cylinders revealed fibre break and delamination. On the other hand, visual examination results show local bucking and brooming failure at the bottom of the cylinders

Prediction of casing critical buckling during shale gas hydraulic fracturing.

Casing deformation during volume fracturing in shale gas horizontal wells is caused by both existing and induced stresses. These stresses jointly alter and compound the stress field around the casing leading to inefficient well stimulation as planned, lack of access into the well for recompletion, future workovers and present imminent danger of well integrity. Using two simulation scenarios, casing structural integrity was investigated in both radial and axial configurations under the mechanics of a combine system - casing, cement and formation rock. Results obtained show that time dependent rock slippage - creep during stimulation lead to an increase transverse displacement and corresponding stresses on the casing. In addition, the effect of combined loading results in significant increase in both displacements and stresses that can cause radial and axial permanent failure of the casing. This explains the lack of access into the casing during multi-stage hydraulic fracturing and future well intervention and recompletions and increased current understating of the downhole dynamics and casing structural integrity during volume fracturing. This new understanding is a major breakthrough in establishing casing health status during shale gas well stimulation

An application of FEA and machine learning for the prediction and optimisation of casing buckling and deformation responses in shale gas wells in an in-situ operation.

This paper proposes a novel way to study the casing structural integrity using two approaches of finite element analysis (FEA) and machine learning. The approach in this study is unique, as it captures the pertinent parameters influencing the casing buckling and the evaluation of the magnitude of each. In this work, the effect of combined loading using multiple parameters to establish the relationship and effect of each on stress, displacement and ultimately casing safety factor is revealed. The optimised result show remarkable improvement in reducing the total deformation, the von Mises and increasing the safety factor of the casing under combined loading condition. The optimised casing shows 89% reduction in total deformation and 87% reduction in von Mises in comparison to unoptimised simulation result. In addition, the safety factor of 3.3 is obtained against the initial predicted stress of 932.46 MPa with a corresponding safety factor of 0.8129. Real time parametric prediction and optimisation using Lunar and Quasar (ODYSSEE software package) enabled the examination of the casing structural responses based on the pertinent parameters. In effect, a very good agreement was found between 'KNN' and Lunar predictions on parameters influencing casing buckling phenomena and the corresponding Mises stress. Lunar optimisation provided the ideal parameter values for the attainment of pre-define von Mises stress as a function of other factors. This quick approach shows both accuracy and validation of the two independent procedures arriving at the same conclusion. We found that concurrent investigation of the casing buckling attributing factors and optimisation using FEA and ODYSSEE package is sufficient to maintain casing structural integrity during shale gas extraction process